1. Field of the Invention
This invention relates to correcting vision defects, such as myopia, and more particularly to changing the radius of curvature of the cornea.
In the normal eye visual perception involves the process of light entering the eye, passing through the cornea and lens converging on the retina at the back of the eyeball. Electrical impulses then transmit a sharp image to the brain.
The common vision problem myopia, or nearsightedness, is a congenital refractive error manifesting itself in the eye's inability to focus light images directly on the retina. Due to the eyeball either being too long or the cornea too curved, the light rays entering the eye converge in front of the retina resulting in the transmission of the brain an "out of focus" image ranging in severity from a mild inconvenience to a debilitating handicap. Ordinarily, myopia can be corrected by corrective lenses, such as eye glasses or contact lenses. However, for many people corrective eyewear is a handicap. Also, when the myopia problem of the eye is the result of a progressive disease such as keratoconus, corrective eye glasses are satisfactory only in the early phases of the disease. Later, when the protrusion of the cornea advances further, contact lens fitting becomes more and more difficult, ultimately necessitating surgery as the only treatment of choice for sight restoration.
2. Description of the Prior Art
Various approaches and devices have been utilized by the prior art for correcting corneal curvature and associated conditions such as myopia, astigmatism and keratoconus. Such approaches included implantation of artificial lenses, implantation of donor's cornea, surgical incisions into the anterior cornea, radio frequency probes, lasers and the like.
One very promising surgical procedure for correcting corneal curvature is radial keratotomy which consists of a series of microsurgical incisions, placed in a radial pattern on the surface of the cornea. The rational for the procedure is as follows. The cornea, being of a dome shape, is being supported by both the limbus and the intraocular pressure. As a result of the microsurgical incisions, the integrity of the cornea decreases resulting in stretching and flattening under the influence of the intraocular pressure. Although initially there appears to be peripheral bulging with central flattening, upon completion of healing the cornea becomes smooth, uniform and as strong as it was prior to the operation. In reducing the curvature of the cornea the result is an improved focusing of the light rays on the retina hence reduction or elimination of myopia. There are, however, clinical variables which influence the success of the surgical procedure, such as intraocular pressure, the radius of corneal curvature and the number of depth of microsurgical incisions made on the cornea. The precise measurement of the variables that affect the outcome is difficult at best. Often, it becomes necessary to repeat the operation in order to further reduce the curvature of the cornea and improve "focusing". One of the most sophisticated techniques in controlling the clinical variables includes the utilization of a special micrometric knife which makes it possible to regulate the incision depth with high precision. The necessary depth of the incision is set according to the degree of myopia, corneal thickness and rigidity, and corneal curvature radius. The expected effect of surgery, given the diameter of the central optical zone, number of incisions and their depth, can then be predicted preoperatively by a computer. While this surgical procedure utilizing the latest instrumental techniques has proved more successful than previous techniques, the lack of predictability of the shape and curvature of the cornea still persists. Obtaining the proper diopter correction is still "an art" and after the healing of the cornea the patient may still be required to wear eye or contact lenses. This lack of reliable predictability greatly hinders the use of this surgical procedure except in serious cases where no other intervention is available.
It is therefore an object of the present invention to provide a reliable method for vision correction.